Brute Rationality is a remarkable book. It is elegant and engaging, and it aims to deliver straightforward solutions to problems not addressed by other theories of practical rationality. The theory of normative reasons developed in Brute Rationality is both detailed and novel. According to Gert, most of the literature on this topic has gone badly wrong by assuming that reasons can only have what Gert calls a 'requiring role.' To assume that reasons have only a requiring role is to be committed to the following type of inference: if the fact that I have a beautiful voice is a reason for me to sing now, I am rationally required to sing now, unless there's a stronger reason for me to do something that is incompatible with my singing now. According to Gert, theories of practical reason committed to this assumption have overlooked the fact that reasons can also have a justifying role. It might be the case, for instance, that my having a beautiful voice justifies, but does not require, my singing on certain occasions. If so, Gert maintains, the following will be true. First, this reason is capable of making a certain action (say, my singing now) [End Page 153] rational where it would have been irrational in the absence of this reason.2 But in contrast with most views of rationality, my failing to act in accordance with this reason would not render my actions irrational even in the absence of countervailing reasons. That is, since my reason to sing does not have a requiring role, if I don't sing, I am not failing to do anything that I am rationally required to do. So no matter what other reasons I may or may not have, I am not being irrational when I choose to let my beautiful voice remain dormant. Moreover, reasons can have differing strengths along the requiring and justifying dimensions. Roughly speaking, my reason to see the aurora borealis can be very weak along the requiring dimension, since I might not be rationally required to do almost anything to see them, but very strong in the justifying dimension, since it might be the case that I would not be irrational if I were to use up all of my vacation time and a good chunk of my savings to take a trip to the Yukon in order to witness this phenomenon. Although this might seem at first a minor correction to orthodoxy, Gert makes a compelling a case that wide-ranging consequences follow from accepting that reasons can have these two distinctive roles, and in the course of making the case for his view, Gert touches on almost every major debate in the area. For instance, Gert argues for (i) a new way of making a distinction between objective and subjective rationality, defending a reliabilist view of the latter (ch. 7); (ii) against the seemingly obvious claim that practical reasons necessarily motivate an agent insofar as she is rational (ch. 3); (iii) for the claim that it is neither rationally required nor irrational to act morally (ch. 2); (iv) for a functional analysis of reasons in terms of their systematic contribution to the rational status of actions (ch. 4); and (v) for a substantive theory of objective reasons in terms of harms and benefits to oneself and others, in which typically only harms and benefits to oneself are (significantly strong) reasons along the requiring dimension, whereas harms and benefits to others are just as strong reasons along the justifying dimension as similar harms and benefits to oneself (ch. 5).

Gert makes original contributions to all the topics he discusses. However, my focus here will be on what is perhaps the central idea of the book: the claim that philosophers have overlooked the need to distinguish between these two different roles that reasons can play, a justifying and a requiring role.3...

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